Psychological factors — Psychological issues such as depression, anxiety, guilt or fear can sometimes cause sexual problems. At one time, these factors were thought to be the major cause of impotence. Doctors now know that physical factors cause impotence in most men with the problem. However, embarrassment or "performance anxiety" can make a physical problem worse.
All NOS subtypes produce NO, but each may play a different biologic role in various tissues. nNOS and eNOS are considered constitutive forms because they share biochemical features: They are calcium-dependent, they require calmodulin and reduced nicotinamide adenine dinucleotide phosphate for catalytic activity, and they are competitively inhibited by arginine derivatives. nNOS is involved in the regulation of neurotransmission, and eNOS is involved in the regulation of blood flow.
Pills such as Viagra® are the most common ED treatment, but they don’t work for everyone. Some guys find they cause bothersome headaches or persistent stomach troubles. Some have serious side effects such as chest pain and vision or hearing changes. Others don’t respond to the medication at all. And still others don’t like having to wait for the pill to take effect.

Watts and coworkers, in their review article, make several points about this ED/CAD nexus. Endothelial dysfunction is present in both CVD and ED, and is linked through the NO mechanism. The authors note that PDE5 inhibitors improve endothelial function and have a salutary effect on both CVD and ED. Both ED and cardiac disease respond to modifications in lifestyle as well as pharmacologic manipulation. These authors also report that the presence of ED gives the clinician an opportunity to assess CVD and prevention as well.20

The main medical causes of erectile dysfunction are based around poor blood flow (due to furring of the arteries thanks to raised cholesterol or high blood pressure), poor nerve supply caused by diabetes-related nerve damage, or low testosterone as a result of obesity, old age or failing gonads. We doctors get just as concerned with men who have variable erections as well as those that can't get an erection at all. Failing to get an erection occasionally is pretty normal as you get older. But if you have unreliable erections for a prolonged period of time – more than six months – this could suggest an early sign of physical problems such as cardiovascular disease or diabetes which could develop further so get yourself checked out.

Chronic stress dumps adrenaline in your system multiple times a day. And that can lead to high blood pressure, heart disease, obesity, and diabetes. Chronic stress is like red-lining your car all day long. When you drive 100 mph all the time, something is going to break down. A high-stress environment can actually change the way your brain sends messages to your body. Dumping too much adrenaline into your bloodstream can affect blood flow and severely limit your ability to achieve and maintain an erection.

A rigid or nearly rigid erectile response to intracavernous injection of pharmacologic test doses of a vasodilating agent (see below) indicates adequate arterial and veno-occlusive function. This suggests that the patient may be a suitable candidate for a trial of penile injection therapy. Genital stimulation may be of use in increasing the erectile response in this setting. This diagnostic technique also may be used to differentiate a vascular from a primarily neuropathic or psychogenic etiology. Patients who have an inadequate response to intracavernous pharmacologic injection may be candidates for further vascular testing. It should be recognized, however, that failure to respond adequately may not indicate vascular insufficiency but can be caused by patient anxiety or discomfort. The number of patients who may benefit from more extensive vascular testing is small, but includes young men with a history of significant perineal or pelvic trauma, who may have anatomic arterial blockage (either alone or with neurologic deficit) to account for erectile dysfunction.
Tadalafil (Cialis) is the third oral medicine approved by the U.S. FDA for the treatment of erectile dysfunction. Like sildenafil (Viagra) and vardenafil (Levitra), tadalafil inhibits PDE5 (as described earlier). Unlike the other PDE 5 inhibitors, patients should take tadalafil once daily and is approved for the treatment of BPH (benign enlargement of the prostate).

Besides treating the underlying causes such as potassium deficiency or arsenic contamination of drinking water, the first line treatment of erectile dysfunction consists of a trial of PDE5 inhibitor (such as sildenafil). In some cases, treatment can involve prostaglandin tablets in the urethra, injections into the penis, a penile prosthesis, a penis pump or vascular reconstructive surgery.[1]